1. Field of the Invention
The present invention relates to a transmission rate control method for controlling a transmission rate of uplink user which is transmitted from a mobile station via an Enhanced Dedicated Physical Data Channel, and a radio base station and a radio network controller used in the transmission rate control method.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”,
Referring to FIG. 3, the mobile communication system, to which the “Enhanced Uplink” is applied, will be described.
In an example of FIG. 3, the cell #1 controlled by the radio base station Node B is a serving cell for a mobile station UE #1, which mainly controls the transmission rate of the uplink user data transmitted by the mobile station UE #1.
In addition, the cell #1 controlled by the radio base station Node B is not a serving cell for the mobile station UE #2 but a non-serving cell for the mobile station UE #2, which establishes a radio link with the mobile station UE #2.
In the above mobile communication system, the cell #1 is configured to transmit, to the mobile station UE #1, an “Enhanced Absolute Grant Channel (E-AGCH: absolute transmission rate control channel)” for transmitting an absolute transmission rate of the uplink user data.
In addition, the cell #1 is configured to transmit, to the mobile station CE #2, an “Enhanced Relative Grant Channel (E-RGCH: relative transmission rate control channel)” for transmitting a relative transmission rate of the uplink user data (for example, up Command, Down Command, Don't care command).
Further, in the above mobile communication system, both of the mobile station UE #1 and the mobile station UE #2 are configured to transmit an “Enhanced Dedicated Physical Control Channel (E-DPCCH)” and an “Enhanced Dedicated Physical Data Channel (E-DPDCH)”.
Here, the cell #1 controlled by the radio base station Node B is configured to transmit a “Down Command” using the E-RGCH in order to minimize the interference from non-serving mobile station (the mobile station UE #2 in FIG. 3).
More specifically, the cell #1 is configured to transmit a “Down Command” using the E-RGCH, so as to hold a ratio of a reception power of the E-DPDCH from the serving mobile station (the mobile station UE #1 in FIG. 3) and a reception power of the E-DPDCH from the non-serving mobile station (i.e., interference power) less than or equal to the predetermined threshold.
Here, the serving mobile station for the cell #1 means the mobile station which sets the cell #1 as the serving cell, and the non-serving mobile stations mean the mobile stations which do not set the cell #1 as the serving cell.
In other word, in the above mobile communication system, MAC functions implemented in the radio base station Node B is configured to control a transmission rate of uplink user data of the mobile station UE using the E-AGCH and the E-RGCH.
However, in the above mobile communication system, the cell #1 controlled by the radio base station Node B is configured to measure the reception power of the E-DPDCH without knowing the patterns of uplink user data to be transmitted via the E-DPDCH. Thus, a huge measurement error can be happen in the above mobile communication system.
Accordingly, in the above mobile communication system, there has been a problem that it becomes difficult for each cell to adjust the ratio of the reception power of the E-DPDCH from the serving mobile station to the reception power of the E-DPDCH from the non-serving mobile station, due to the measurement error, and therefore, transmission efficiency is decreased.